Résumé : Classic physics text-books teach that the sign of the Hall-coefficient tells one the sign of the charge carrier. However metamaterials of interlinked rings provide a counterexample. This has been shown theoretically, numerically, and experimentally. Additionally, metamaterials allow one to create Hall-effect materials where the electric field generated by the Hall voltage is parallel to the magnetic field - the so-called parallel Hall effect. Here we will review these results and also provide some completely novel geometries that display reversal of the sign of the Hall-coefficient. One reroutes the contacts in the unit cell of periodicity. It achieves at a microscale what at a macroscale can be achieved by crossing the leads that pick up the Hall voltage. Another metamaterial displaying reversal of the sign of the Hall-coefficient reroutes the magnetic field at a microscopic scale through the use of constituents with high magnetic permeability. While these metamaterials operate at low frequency, their analysis opens the door to manipulating Faraday rotation, and the associated non-reciprocal effects that may lead to new optical devices.